The present invention refers to a control mechanism for a fiber feed device on an open-end spinning mechanism, which exhibits a sensor and a switching mechanism which is controlled from the sensor upon drop in the yarn tension. The switching mechanism, in turn, controls the operation of the fiber feed device via a control member.
In tying up the end of yarn carried on a package with the yarn being produced in the rotor of an open end spinning machine, the yarn end from the package follows the lead-back portion into the yarn draw-off tube and into the spinning chamber because of the reduced pressure prevailing in the spinning rotor. The lead-back can in that case be effected in various ways, e.g., by hand or by release of a yarn reserve or by turning back the delivery rollers and the bobbin. Depending upon whether the yarn is thick or thin or to what extent in that case it passes by points of deflection, the suction air flow existing at the mouth of the yarn draw-off tube obtains a different effect. Particularly in the case of fine yarns it occurs again and again that the end of the yarn sticks upon leading back or only follows the lead-back hesitatingly. Faulty joins thereby result upon starting the spinning unit. The yarn sensor has a particularly disadvantageous action here as it forces away the yarn which is not under draw-off tension and hence causes a deflection.
It has therefore already been proposed, for the leading back of the yarn into the spinning mechanism to swing the sensor out of the yarn breakage position into its opposite end position, so that the yarn may be guided back unimpeded into the yarn draw-off tube (West German Pat. No. 1,560,334). Since the sensor controls the feeding of the fiber directly, the disadvantage results that upon the freeing of the lead-back by the position of the sensor the fiber feed does not always get switched on at the required instant. That is, it has been found that for successful joining of the yarn it is extraordinarily important that the fiber feed is matched exactly to the leading back of the yarn so that the led back end of the yarn and a ring of fiber existing in the spinning rotor meet. This matching has to be effected in adaptation to the different materials, thicknesses of yarn, rotor speed, yarn drawn-off speed and possibly differing reduced pressure.
Again, a mechanism is known in which in the position of the sensor in which it is sensing the yarn the fiber feed is switched on, while in the yarn breakage position of the sensor the fiber feed is certainly switched off but by means of an auailiary switch may be switched on again at will (West German O/S No. 2,058,603, FIG. 1). If in the case of this mechanism the sensor is swung over in order to facilitate the introduction or leading back of the yarn into the spinning mechanism, the fiber feed is willy-nilly switched on too.
A mechanism is furthermore known in which the sensor at joining may be brought by a switching unit into the position in which the sensor switches on the fiber feed (West German O/S No. 2,058,603, FIG. 2). In this way the timing of the starting of the fiber feed is again dependent upon the position of the sensor.
The same disadvantage arises if the switch is arranged in a parallel circuit to the yarn monitor (West German O/S No. 2,058,603, Paragraph 2).